1. Field of the Invention
The present invention relates to a device for controlling the rise of the catalyst temperature in a spark ignition-type internal combustion engine to meet exhaust gas regulations and, particularly, to a device for controlling the rise of the catalyst temperature in an internal combustion engine, which is capable of quickly raising the catalyst temperature up to an activating temperature.
2. Prior Art
The exhaust pipe of an internal combustion engine has heretofore been provided with a catalyst for removing exhaust gas components. The catalyst works at an activating temperature. When the internal combustion engine is cold; therefore, the temperature of the catalyst must be raised by, for example, exhaust gases of a high temperature.
In a conventional device for controlling the rise of the catalyst temperature in an internal combustion engine, therefore, a technology has been proposed such as delaying the ignition timing to promote the rise of the catalyst temperature at the start.
In a device for removing exhaust gas components disclosed in, for example, Japanese Unexamined Utility Model Publication (Kokai) No. 79212/1976, the heated secondary air is introduced into the intake system, and the ignition timing is delayed to quickly raise the temperature of the catalyst at the start.
FIG. 38 is a diagram illustrating the constitution of a conventional device for controlling the rise of the catalyst temperature in an internal combustion engine.
FIG. 39 is a diagram illustrating a change in the ratio for removing exhaust gas components relative to the catalyst temperature TC, wherein the abscissa represents the catalyst temperature TC and the ordinate represents the removal ratio [%].
In FIG. 39, a solid line represents a ratio for removing CO (carbon monoxide) and HC (hydrocarbons) and a broken line represents a ratio for removing NOx (nitrogen oxides). When the catalyst temperature TC rises and reaches an activation starting temperature (=130.degree.), the removal ratio starts rising from 0%. When a completely activating temperature (=180.degree. C.) is reached, the removal ratio reaches nearly a maximum value (=98%).
In FIG. 38, the main body of the internal combustion engine 1 is provided with an intake pipe 2 for introducing the air into the engine and an exhaust pipe 3 for exhausting the exhaust gases burnt in the engine 1.
An air cleaner 4 is provided in an upstream portion of the intake pipe 2, and an air flow sensor 5 for detecting the amount Qa of the air taken in by the engine 1 is provided on the downstream side of the air cleaner 4.
A throttle valve 6 is provided in the intake pipe 2 on the downstream side of the air flow sensor 5 to adjust the amount Qa of the air that is taken in.
The intake pipe 2 is further provided with a by-path 7 by-passing the throttle valve 6, and an idling rotational speed control valve (hereinafter referred to as ISC valve) 8 for adjusting the opening degree of the by-path 7.
The ISC valve 8 adjusts the amount of the air taken in by-passing the throttle valve 6, so that the idling rotational speed of the engine 1 is controlled to assume a target value.
The exhaust pipe 3 is provided with an air-to-fuel ratio sensor 9 for detecting the oxygen concentration in the exhaust gases as an air-to-fuel ratio A/F.
On the downstream side of the exhaust pipe 3, furthermore, there are provided catalysts 10 and 11 for removing exhaust gas components relying upon the chemical reaction. The one catalyst 10 is provided in a hanging portion in the exhaust pipe 3 and another catalyst 11 is provided in the exhaust pipe 3 under the floor.
Generally, the catalysts 10 and 11 are called three-way catalysts, and work to oxidize CO and HC, and to reduce NOx, thereby to remove harmful components in the exhaust gases.
An intake portion corresponding to each cylinder of the engine 1 is provided with an injector 12 for injecting the fuel that is sent from a fuel pump (not shown).
The engine 1 is further provided with a crank angle sensor 13 that produces a crank angle signal CA corresponding to the rotational speed Ne of the engine.
Based on the operation condition data (amount Qa of the air taken in, air-to-fuel ratio A/F, crank angle signal CA, etc.) input from the sensors, an electronic control unit (hereinafter referred to as ECU) 14 including a microcomputer operates the control quantity for the engine 1, and produces a fuel injection signal J for driving the injector 12, an ISC control signal C for driving the ISC valve 8, an ignition signal P for driving an ignition device (described later) and the like signals.
Here, though not diagramed, a variety of sensors for detecting the operation conditions of the engine 1 include a water-temperature sensor for detecting the cooling water temperature TW of the engine, an intake-air-temperature sensor for detecting the temperature of the air taken in, and the like sensors.
The ignition device is constituted by spark plugs (not shown) provided in the cylinders of the engine 1, an ignition coil 15 connected to a battery to apply a high voltage to the spark plugs, and an igniter 16 which makes and breaks the spark coil 15 in response to the ignition signal P.
Next, described below is the operation of the conventional device for controlling the rise of the catalyst temperature in an internal combustion engine shown in FIG. 38.
First, the injector 12 injects the fuel of a required amount into the engine 1 depending upon the width of a drive pulse which is a fuel injection signal J. In response to the ignition signal P, furthermore, the igniter 16 makes and breaks the ignition coil 15 to apply a high voltage to the spark plug thereby to ignite the mixture in the cylinder.
At this moment, the amount of fuel injected from the injector 12 is calculated depending upon the amount Qa of the air taken in and the rotational speed Ne of the engine, and is corrected based on the air-to-fuel ratio A/F.
The ignition timing is set based on the amount Qa of the air taken in and the rotational speed Ne of the engine.
As is well known, furthermore, the fuel injection timing and the ignition timing are operated by using a pulse edge (reference crank angle position) of the crank angle signal CA as a timer control reference.
The mixture burnt in the engine 1 is exhausted as exhaust gases through the exhaust pipe 3, and from which harmful components are removed through the catalysts 10 and 11.
The temperature range in which the catalysts 10 and 11 are used is usually from about 130.degree. C. to about 900.degree. C.
When the temperatures of the catalysts 10 and 11 are to be quickly raised, in general, the ignition signal P is corrected by operation and the target ignition timing is corrected toward the delay side as disclosed in the above-mentioned known literature.
Upon delaying the ignition timing, the exhaust gases of a high temperature right after (or during) the combustion are exhausted into the exhaust pipe 3, and the temperatures of the catalysts 10 and 11 are quickly raised from the cold engine temperature up to an activating temperature.
During the idling operation condition, on the other hand, the throttle valve 6 is fully closed and the vehicle comes into a halt. The ECU 14, however, adjusts the opening degree of the ISC valve 8 to control the idling rotational speed.
That is, during the idling operation condition, the ECU 14 operates the amount of the air taken in through the bypath to obtain a target idling rotational speed and produces an ISC control signal C, and further corrects the ISC control signal C based on a deviation between a real engine rotational speed Ne and the target idling rotational speed in order to control the amount of the air taken in through the by-path (to control the opening degree of the ISC valve 8) by feedback.
When the engine 1 is cold, the target idling rotational speed is increased by a predetermined amount (100 rpm to 200 rpm) so that the engine 1 assumes a stable combustion.
In recent years, however, regulations against the exhaust gases have been reinforced as LEVs (low-emission vehicles) have been developed. To cope with the regulations, therefore, the catalyst temperatures must be raised up to the activating temperature more quickly. In quickly activating the catalysts, furthermore, it is required to avoid deterioration in the fuel efficiency and drivability.
According to the conventional device for controlling the rise of catalyst temperature in an internal combustion engine as described above, the temperature of the catalyst could not be very quickly raised despite the ignition timing was corrected toward the delay side and, hence, the exhaust gas components could not be removed to a degree that satisfies the exhaust gas regulations at the start or during the idling operation condition.